ACAPULCO, Mexico -- Top seed and reigning US Open champion Sloane Stephens fended off a difficult challenge by Dutch qualifier Arantxa Rus and propelled herself into the quarterfinals of the Abierto Mexicano TELCEL presentado por HSBC on Wednesday, ultimately prevailing 5-7, 7-6(6), 6-0.

Stephens had to save a match point in the second-set tiebreak before claiming victory in a grueling two hours and 26 minutes, and thus denying the left-hander from the Netherlands her first Top 20 win in over six years.

"Playing a lefty is always tricky," Stephens told the press after the match. "I tend to play a lot of three-setters with lefties, so I knew it was going to be a battle, obviously."

"But I am happy," the No.1 seed continued. "I was match point down, and I was able to come back and fight. For not having played for a while, since Australia, it’s good progress."

The American, who won this title two years ago, now finds herself on a two-match winning streak after not having won a match between her Grand Slam triumph in New York and this week.

The players exchanged breaks at the start of the match, as both combatants were feeling out each other’s games with extended rallies. But after the first two games, each player was able to hold serve up to 5-5 in the set.

At the end of the set, though, it surprisingly was the American who blinked first, as she had not faced a break point since the very first game. But a Stephens backhand went long to give Rus a break point, which she grasped after a Stephens forehand went just wide after another lengthy rally.

The Dutchwoman took advantage of her chance, holding on her first set point when Stephens misfired long on another backhand. Each player had six winners in the first set, but Stephens had two more unforced errors than Rus, and that made the difference down the stretch in the opening frame.

The second set was totally up for grabs. Stephens fended off three break points in the opening game, before breaking Rus in the next game for a 2-0 lead. But consecutive forehand errors by the American allowed Rus to get back on serve in the very next game.

Both players were now cracking their service returns exceptionally well, and when the dust settled after the next five games, Rus was up a break at 5-4, and would serve for the match. But the Dutch qualifier could not hold on, and a strong forehand by Stephens forced Rus into an error, and put the set back at 5-5.

Stephens had a set point at 6-5, but sent a backhand wide, and the women advanced to the tiebreak two points later. Strong defense by Rus gave her the early advantage, and she jumped to a 4-1 lead. Exceptional backhands by the US Open champion knotted the tiebreak at 5-5, but a forehand winner by Rus right on the sideline gave the qualifier a match point at 6-5.

But the championship experience of Stephens paid off on her two service points. A forehand winner pulled the tiebreak to 6-6, and after the change of ends, a solid serve set up another winning point, which led to a second set point for the American. Rus faltered with a rally forehand into the net, and suddenly the match was even at one set apiece.

After that marathon set, the wind went out of the Dutchwoman's sails, and she could only win seven points in the decider as Stephens cruised to the final-set demolition. The No.1 seed finished the match with 20 winners to 16 for the Dutch qualifier, and Rus ended up with two more unforced errors than the American.

Stephens advances to her first quarterfinal since her title run at the US Open, where she will face Switzerland's Stefanie Voegele, who beat Greece's Maria Sakkari, 6-3 6-4.

Defending champion Lesia Tsurenko leads a group of other early winners today, as the No.7 seed from Ukraine ousted Australian Arina Rodionova, 6-3, 6-1. In other results, Paraguay's Veronica Cepede Royg upset 5th-seeded Romania Irina-Camelia Begu, 7-6(3), 6-1, and No.3 seed Daria Gavrilova of Australia defeated Mexican Renata Zarazúa, 7-5, 6-3.